Surface activation by plasma jets for thermal spray coating on cylinder bores

Abstract

A method of activating the surface of an aluminum-based substrate. This method includes cleaning the substrate surface, and operating a plasma spraying device such that a air plasma jet produced by the device is accelerated toward the surface so that it removes or decomposes any remaining oxides and other surface contaminants. In one form, the surface being treated forms part of a cylinder bore of an internal combustion engine block. In a particular form where a protective coating is subsequently being applied to the substrate, a sequential series of plasma spraying devices may be used such that a first—preferably simpler—device is used to perform activation or pretreatment operations, while a second—and more comprehensive—device may be used to deposit the protective layer on the pretreated surface.

What is claimed is: 
     
         1 . A method of activating the surface substrate of an aluminum-based engine cylinder bore to achieve better adhesion between a subsequently-applied protective coating and the substrate, said method comprising:
 cleaning said surface to remove at least a portion of an oxide formed thereon; and   operating a plasma spraying device such that an air plasma jet produced thereby impinges on said surface.   
     
     
         2 . The method of  claim 1 , wherein said plasma spraying device defines a pretreatment plasma spraying device that is separate from a plasma spraying device used to deposit a protective coating on said surface. 
     
     
         3 . The method of  claim 2 , wherein said pretreatment plasma spraying device is configured such that it is incapable of receiving a protective coating material precursor therein. 
     
     
         4 . The method of  claim 1 , wherein said activating is accomplished without said surface being subjected to separate mechanical activation step. 
     
     
         5 . The method of  claim 1 , wherein said cleaning comprises exposing said surface to a potassium-fluoride solution such that at least one compound containing potassium, aluminum and fluorine is formed on said surface. 
     
     
         6 . The method of  claim 5 , wherein said at least one compound containing potassium, aluminum and fluorine comprises at least one of K 3 AlF 6  and KAlF 4 . 
     
     
         7 . The method of  claim 1 , wherein said cleaning comprises exposing said surface to an acid solution. 
     
     
         8 . The method of  claim 7 , wherein said acid solution comprises nitric acid. 
     
     
         9 . The method of  claim 8 , wherein said nitric acid solution further comprises at least one of hydrofluoric acid and a fluoride salt. 
     
     
         10 . The method of  claim 9 , further comprising rinsing said surface after each exposure to said nitric acid solution. 
     
     
         11 . The method of  claim 1 , further comprising depositing a protective coating material precursor onto said surface once said activating is substantially complete. 
     
     
         12 . The method of  claim 11 , wherein said depositing a protective coating material precursor onto said surface is performed by plasma spraying. 
     
     
         13 . A method of coating the surface of an aluminum-based substrate, said method comprising:
 cleaning said surface to remove at least a portion of an oxide formed thereon;   operating a first plasma spraying device such that an air plasma jet produced thereby impinges on said cleaned surface; and   operating a second plasma spraying device such that a protective coating material precursor introduced therein impinges on said cleaned surface that has been pretreated with said air plasma jet.   
     
     
         14 . The method of  claim 13 , wherein said surface defines an engine cylinder bore. 
     
     
         15 . The method of  claim 14 , wherein said first plasma spraying device is configured to operate to not introduce a protective coating material precursor therein. 
     
     
         16 . The method of  claim 13 , wherein said operating a first plasma spraying device takes place at a lower power setting than said operating a second plasma spraying device. 
     
     
         17 . A method of coating a cylinder bore of an engine block, said method comprising:
 cleaning said surface with a solution containing at least one of potassium and fluorine;   operating a first plasma spraying device such that a pretreatment plasma jet produced thereby impinges on said cleaned surface; and   operating a second plasma spraying device such that a protective coating material precursor introduced therein impinges on said pretreated surface.   
     
     
         18 . The method of  claim 17 , wherein said pretreatment plasma jet produced by said first plasma spraying device is an air plasma, and wherein said plasma coating produced by said second plasma spraying devices includes at least one of argon, hydrogen and helium.